Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $92.88   5.860%   $98.3228   $98.32   $98.30   $98.30  
  Purchase #2 $177.43   8.868%   $193.1645   $193.16   $193.15   $193.20  
  Purchase #3 $14.86   9.146%   $16.2191   $16.22   $16.20   $16.20  
  Purchase #4 $248.93   7.544%   $267.7093   $267.71   $267.70   $267.70  
  Purchase #5 $183.44   13.120%   $207.5073   $207.51   $207.50   $207.50  
  Purchase #6 $199.60   3.709%   $207.0032   $207.00   $207.00   $207.00  
  Purchase #7 $63.47   11.764%   $70.9366   $70.94   $70.95   $70.90  
  7 purchase totals = $980.61       $1,060.8628   $1,060.86   $1,060.80   $1,060.80